This invention relates to pneumatically operated impact drilling tools for rotary drilling having an improved system of valving.
There are currently many pneumatic impact drilling tools used in the field. A typical such device is disclosed in U.S. Pat. No. 3,964,551 which patent is hereby incorporated by reference.
The importance of simplicity and durability of construction in a pneumatic impact drilling tool cannot be overemphasized. The expenses involved in maintaining drilling rigs, paying skilled crews, and other time-related expenses, make it mandatory that "down-time" be held to an absolute minimum. A second essential consideration in drilling tool design is drilling rate (feet of hole drilled per unit time). This is basically related to the force of each individual hammer impact, and the frequency with which they occur.
Another prospect for time savings lies in the area of maintenance procedures; tool design should eliminate maintenance wherever possible. Required procedures, such as changing worn out drilling bits, need to be simple and fast.
Manufacturing cost is also important to a designer of down hole drilling tools, in that use of exotic materials and/or manufacturing procedures might price an otherwise satisfactory tool out of the market.
There is a constant need in the impact drilling industry for improvement in any or all of the aforementioned areas (reliability, drilling rate, maintenance, cost). Significant contributions in one or more will improve the performance of the industry and help in the economic utilization of our natural resources.